Method for preparing porous titania thin film by using cellulose nanocrystal

Abstract

The present invention relates to a composite material including a porous titania thin film and a preparation method therefor. A composite material according to the present invention allows for a simple thin film formation process because of the use of cellulose crystals, makes it easy to control the structure of the titanium dioxide thin film provided therefor, has a large specific area, and is superior in terms of scratch resistance and photoactivity, thus finding useful applications in the various fields utilizing titanium dioxide as a photocatalyst.

The invention claimed is: 
     
       1. A method of preparing a composite material, comprising:
 applying a mixture including a titanium dioxide precursor, cellulose crystals, and one or more transition metals compound onto a substrate; and 
 thermally treating the applied mixture to form a titanium dioxide thin film, 
 wherein the thin film includes titanium dioxide doped with the one or more transition metals selected from the group consisting of molybdenum (Mo), niobium (Nb), tungsten (W), iron (Fe), and silver (Ag), 
 wherein the cellulose crystals have an average length of 150 nm to 500 nm, 
 wherein the titanium dioxide thin film has a harness of 10 N to 50 N, 
 wherein the thin film includes a pore satisfying conditions of Expressions 1 and 2 below:
   150≤ L≤ 300  [Expression 1]
 
   15 ≤L/D ≤70  [Expression 2]
 
 
 In Expressions 1 and 2, 
 L represents an average size in a longitudinal direction of a pore, 
 D represents an average size in a thickness direction of a pore, and 
 L and D are indicated in units of nm. 
 
     
     
       2. The method of  claim 1 , wherein the titanium dioxide precursor includes a tetravalent titanium ion (Ti 4+ ). 
     
     
       3. The method of  claim 1 , wherein the titanium dioxide precursor is one or more selected from the group consisting of titanium tetraisopropoxide, titanium ethoxide, titanium butoxide, and titanium tetrachloride. 
     
     
       4. The method of  claim 1 , wherein the cellulose crystals are cellulose nanocrystals (CNC), and the titanium dioxide precursor is included in the mixture in such a way that a weight ratio (Ti 4+ /CNC) of the tetravalent titanium ion (Ti 4+ ) included in the titanium dioxide precursor to the cellulose nanocrystal (CNC) is 0.1 to 10. 
     
     
       5. The method of  claim 1 , wherein the cellulose crystal has an average diameter of 0.1 nm to 10 nm. 
     
     
       6. The method of  claim 1 , wherein the mixture further includes a 35±3 wt % hydrochloric acid aqueous solution at 50 to 90 parts by weight with respect to 100 parts by weight of the titanium dioxide precursor. 
     
     
       7. The method of  claim 1 , wherein the thermal treatment is carried out at a temperature ranging from 300° C. to 600° C. for 10 minutes to 100 minutes.